Almost 700,000 children in the UK may be acting as carers for parents or other relatives, according to research published tomorrow. The figure is four times more than previously thought. The BBC surveyed more than 4,000 secondary school pupils using a specially-designed psychometric test. They found an "invisible army" – totalling 8% of those tested – were taking on caring roles, which included helping someone dress, bathe or shower. The number of young carers had been estimated at only 175,000, or 2%, based on the 2001 census, which had to be filled in by parents.

Academics who developed the 18-item questionnaire said the stigma of admitting some disabilities and that their children were helping look after them, meant that the census was always likely to under-represent the true figures.

Professor Saul Becker, from Nottingham University's school of sociology, said: "The figures are a wake-up call to governments, carers' organisations, civil society as a whole, that in our midst are many children who are providing care to family members, often at the expense of their own childhood. Is this a situation that we can tolerate in our society, that children are giving up to a large extent, their childhood?"

The National Young Carers Coalition (NYCC) said it had long known that the census figures were a vast underestimate, and feared for young carers as public sector cuts kicked in. It also believes there are many more young carers than the 700,000 estimated by the new survey.

"Despite this staggering increase in numbers, there will be a significant decrease in services to support them and their families," said a NYCC a spokesperson. "Young carers need to be identified and supported early before caring causes damage to their health and wellbeing. Often just a small amount of help, put into place early enough, can significantly reduce a caring role and help young carers to cope."

The spokesperson added: "With cuts to local services, social workers and health professionals will be less able to act preventatively. They will be forced instead to support those young carers – and their families – who are already in crisis and who are deeply entrenched in inappropriate caring roles."